Soldering iron



United States Patent Inventor Paul Gotley Essex, England Appl. No. 647,656 Filed June 21, 1967 Patented Dec. 29, 1970 Assignee Electrical Remote Control Company Limited Essex, England Priority Dec. 30, 1966 Great Britain No. 58,478/66 SOLDERlNG IRON 13 Claims, 3 Drawing Figs.

US. Cl 219/241, 219/236, 219/501, 219/505: 307/305, 307/310: 323/22 Int. Cl HOSb 1/02, B23k 3/04 Field of Search 219/241,

501, 236, 504, 505; 236/(SL'R Digest): 323/225SCR; 307/305, 310

Primary Examiner- A. Bartis Attorney-Waters, Roditi, Schwartz & Nissen ABSTRACT: A soldering iron has a soldering bit carried by a handle and a heating element and a temperature-sensing element for the bit. The handle contains bit temperature control circuitry connected to the heating element and the sensing element. The heating element is in series with a thyristor and the sensing element is in series with resistance to provide a voltage divider the tap of which is connected to the control electrode of the thyristor. Delay circuitry may be connected between the tap and the control electrode to render the soldering iron applicable to a wide range of operating voltages.

SOLDERING IRON BACKGROUND OF THE INVENTION This invention relates to soldering irons.

Soldering irons conventionally comprise a handle, a stem and a soldering bit connected, normally releasably, to the stem. An electrical-heating element is provided for heating the bit. When the element is connected to an electrical supply, but soldering is not carried out, the bit temperature rises considerably above the most desirablesoldering temperature. Furthermore, when soldering is carried out, the bit temperature fall rapidly below the most desirable soldering temperature.

SUMMARY 7 The invention provides an electrical soldering iron comprising: a handle; an soldering bit connected to said handle; electrical supply conductors; a first and a second circuit path connected to said conductors; a heating element for said bit and connected in said first circuit path; and controllable impedance solid state semiconductor device connected in series with said heating element in said first circuit path having an impedance which depends upon the current magnitude in said second circuit path; and a temperaturesensing element physi v cally positioned in the region of said heating element, electri- DESCRIPTION OF DRAWINGS In order that the invention may be clearly understood an readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

FIG. 1 shows a diagrammatic longitudinal sectional view of the bit end of an electric soldering iron and an electrical circuit thereof;

FIG. 2 shows a modified version of .the electrical circuit of FIG. I; and 7 FIG. 3 is a sectional view taken along line A-A in FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, the soldering iron has a handle 1A to which is attached a tubular stem 1. The stem has been formed from rolled sheet material of poor thermal conductivity, for example stainless steel, so that the stem has a longitudinal slot 2 extending the whole length of the stem and from the outer periphery thereof to the inner periphery thereof. Loosely fitted, preferably push-fitted, over the outer end of the stem 1 is a one-piece copper bit 3 consisting of a solid part 4 and a sleevelike part 5 integral with the inner end of thepart 4. Inside the free end of the stem is an electrical-heating element 6 the whole, or the major part, of which is surrounded by the bit 3. On engergization of the heating element 6, the stem 1 opens out in the sense of widening of the slot 2 unitl the free end of the stem engages tightly within the sleeve 5. On deenergization of the heating element, the stem 1 closes up in the sense of narrowing of the slot 2 so that the free end of the stem 1 is only loosely situated within the sleeve 5. This arrangement has the advantages that the bit 3 is easily removable but will not fall from the stem when the bit is hot, and that the soldering irondcan be more simply and more economically manufacture The element 6 is in the fonn of a tube coaxial with the stem 1 and consists of a helical coil 7 embedded in electrical insulation 8. ln manufacture of the element a helical coil of high-resistance wire has deposited thereon by electrophoresis and aluminum compound and then the coil and the compound are fired to produce a hard electrical insulation surrounding the wire. Leads are welded to both ends of the coil, the element 6 is inserted into the stem 1 and an electrical temperaturesensing element 22 (a thermistor) is inserted into the element 7 6. The element 22 may alternatively consist of a ceramic core on which is wound a helical coil of fine-gauge wire having its ends welded to leads. Although for ease of illustration the leads are shown as extending laterally from the elements 6 and 22, it will be appreciated that the leads in fact extend in an electrically insulated manner within the stem l to the handle of the soldering iron. The insulation 8 insulates the coil 7 from both the stem 1 and the thermistor 22. The described method of manufacture of the element 6 is both easy and economical. If desired, the coil 7 can instead have its axis of serpentine form. The heating coil 7 is connected across the terminals L and N by a solid state semiconductor device, here a silicon controlled rectifier 21 acting as a switch.'A series arrangement of a diode 23, a fixed resistance 24, a trimmer resistance 25 and a variable resistance 20 are connected between theanode and gate electrodes of the rectifier 21.

For an operating voltage of 24 v., typical values are 50 k (I. for the resistances 20 and 25, 25 k (I for the resistance 24 and k!) cold resistance for the thermistor. The thermistor is connected between the gate electrode and the terminal N.

When the iron is cold the thermistor will have a cold resistance of the order of 100,000ohms. When alternating voltage is applied to terminals L and N current will commence to flow during alternate half cycles through terminal L, coil 7, diode 23, resistance chain 24, 25 and 20 and thermistor 22 to terminal N. The thermistor, at this stage, has a very high resistance compared with that of the resistances 24, 25 and 20 in series. As soon as the voltage between terminals L and it reaches approximately 2 v. in the first half cycle, the gate electrode will have sufficient voltage to fire the silicon controlled rectifier 21. Immediately rectifier 21 is fired, the voltage drop across the rectifier is reduced to approximately /2v., i.e. its forward voltage drop. The fired rectifier 21 will of course for all practical purposes short circuit the resistance chain. This reduces immediately the power consumption in the control circuit.

Consequently the soldering iron is heated, but there is virtually no power dissipation in the handle of the soldering iron where the diode 23, resistance 20, 24 and 25, the rectifier 2l and a condenser 26 are located. The heating element 7 and the thermistor 22 are located inside the soldering iron stem.

When the applied alternating voltage is passing through the second half of its cycle, the polarity of terminal N with respect to terminal 1 is reversed and virtually no current at all will flow. Accordingly, the current wave form applied to the element under these conditions is approximately a half wave rectified sinusoldal wave form.

It is possible to provide full wave heating of the element by increasing the number of control elements but at the same time heat dissipation in the handle of the soldering iron would be increased. a

As the soldering element heats up by virtue of energization in alternate half-cycles, the resistance of the thermistor rapidly falls. At a typicalcontrolled temperature of say 250 C., the resistance of the thermistor might be only of the order of 30 ohms. When this condition is reached, the gate-tocathode voltage of the rectifier 21 never increases sufficiently to fire the rectifier. Under these conditions, only a minute current is flowing through the soldering iron element 7, the same current passing also through the resistance chain and thus causing a small dissipation of heat in the handle of the soldering iron.

Using a typical soldering iron with an element developing a power of approximately 40 watts, the heating up and cooling down rate of the soldering iron is such that the rectifier 21 goes from its fully on state to its substantially nonconducting state in a matter of seconds. i

temperature of the thermistor and by the resistance chain in-- t cluding the resistance 20.

The adjustable resistance therefore provides a controlledsetting of the mean soldering iron temperature and will be provided with a visible temperature scale calibrated correctly at the factory by resistance 25.

,The ranges of component values indicated apply to soldering irqaoperating from a low voltage source of, say,'24 v.- 50

c/s. For direct operation from a mains supply, component values will have to be altered accordingly, of course,

FIG. 2 2 illustrates a-modification in'which the circuit is adapted for use over'a wide range of voltages without adjustment. ln this embodiment, this adaptability is achieved by having the rectifier nonconductive through the peak regions of applied voltage. For this purpose the rectifier is fired inthe latter half of alternate half-cycles so as only to pass current during the fall towards-zero of theapplied voltage. Th'is is achieved by employing a phase-shift circuit 27, consisting in this case of a resistance-capacitance network, connected between the gate electrode and the junction of resistance 20 and thermistor 22. Accordingly the phase delay will be greater than 11/2 at the rated frequency, i.e. greater than a two hundredth of a second, but less than one hundredth of a second at 50 c/s. I

Iclaim:

1. An electrical-soldering iron comprising: a handle; a 501- dering bit connected to said handle; electrical supply conductors; a first circuit connected to said conductor; a heating element for said bit and connected in said first circuit; controllable semiconductor rectifier means having an anode, a cathode and "a gate with the anode to cathode path lof said rectifier means connected in series with-said heating element in said firstrcircuit; a'second; gating, circuit connected ,across said rectifier means for firing angle control of said rectifier means;-

a rectifier connected to produce unidirectional current flow in said'second circuit; a voltage divider in said secondcircuit and providing a tap; a constant impedance direct-current path connecting said tap and said gate; and a temperature-sensing element physically positioned in the region of said heating element, electrically connected as part of said voltage divider and having an impedance 'which varies with heating element temperature to cause said temperature to vary within a predetermined temperature range by firing angle controlof said rectifier means.

2. A soldering iron according .to. claim" 1 wherein said second circuit is connected between saidanode and said cathode of said rectifier means and-the parallel arrangement of said second circuit and saidtifec tifier means is COHI'ICCICdqIO said conductors via said heating element-.- r g;

3,-A soldering iron according to claim 2 wherein aid;, voltage divider consists of said sensing-element and a resistance.

4.-; A soldering iron according to-claim 3 wherein said -resistance is variable for presetting said temperature range.

SitA soldering iron according to claim 3 wherein one end of said sensing element is connected to said cathode and the other to said gate via said direct-current path.

6. A soldering iron according to claim 1 wherein said directcurrent path is provided by a direct connection.

7. A soldering iron according to claim lwherein said directcurrent path is provided by a resistance.

' -8.' A soldering iron according to claim 1, and including; delay means for delaying the striking of said rectifier means so that said striking will occur in the latter half of a half cycle of altemating'voltage, at a predetermined operating frequency,

applied to said supply conductors.

9. A soldering iron according to claim 8 wherein said delay means has a delay of more than a quarter of a cycle at an operating frequency of 50 c/s. l

10. A soldering iron according to claim 5 comprising dela means connected between said tap and said gate for delaying the striking of said rectifier means so that said striking will occur m the latter half of a half cycle of alternating voltage. at 

